An embodiment of the invention relates generally to the field of semiconductor technology and, more specifically, to the formation of interconnects in an integrated circuit.
In the formation of electronic circuitry, electromigration of metal interconnects must be considered. FIG. 1 illustrates a metal interconnect formed according to a conventional technique. Referring to FIG. 1, an interlayer dielectric (ILD) 102 is deposited on an etch-stop layer 104, typically silicon nitride. A via 106 and trench 107 are patterned into the ILD 102 according to well-known dual damascene techniques. A barrier layer 108 may be formed on the bottom and sidewalls of the via 106 and the trench 107. The via 106 and trench 107 are then filled with an electrically conductive material, such as copper and planarized to the top of the ILD 102, thus forming a copper interconnect 110. An etch-stop layer 112, is deposited over the planarized ILD 102, the planarized barrier layer 108, and the planarized interconnect 110. Consequently, a second ILD 114, second barrier layer 118, and second interconnect 116 may be formed, the second barrier layer 118 and second interconnect 116 connecting to the first interconnect 110 to provide electrical connection between interconnects 110 and 116. The process may repeat itself for additional ILD/ interconnect layers.
The typical copper interconnect shown in FIG. 1 suffers from problems. As current flows through the copper interconnect 110, the force of the flowing electrons in the current dislodges copper ions within the interconnect 110, a phenomena generally known as xe2x80x9celectromigrationxe2x80x9d. The dislodged copper ions tend to migrate in a direction that has the least resistance to their movement. The interface 120 between the top of the copper interconnect 110 with the bottom of the etch-stop layer 112 is commonly the area of least resistance. In other words, the etch-stop layer 112 does not significantly prevent electromigration at the top of the interconnect 110.
As integrated circuits become smaller in size, interconnects must also become smaller. Consequently, modern interconnects must have higher current densities to maintain proper electrical performance. Unfortunately, the higher that an interconnect""s current density increases, so does the tendency to cause electromigration at the top of the interconnect 110. In other words, because of the increased density of modern interconnects, dislodged ions will be even more inclined to seek paths of least resistance than in the past, thus increasing the tendency for electromigration to occur at the top of interconnect 110. Because the top of the interconnect is especially vulnerable to the electromigration effect, modern interconnects are suffering electromigration at the top more severely than in the past.
Some attempts have been made to address this problem, such as doping, cleaning, or roughening the top of the copper interconnect. However these approaches result in limited gains for electromigration performance and low adhesion strengths or tend to contaminate the entire interconnect with a dopant species resulting in a high electrical resistivity.